The present application relates to underwater borehole systems, and in particular to distributed marinized borehole systems.
Boreholes for extracting oil, gas, or other fluids or mixtures are formed in earth formations by drilling into the earth formation. Drilling mud may used to control conditions in the borehole, and in an underwater borehole environment, pipes typically extend from platforms on a surface of the borehole to the floor of a body of water to transmit the drilling mud to the borehole. Likewise, during and after completion of the borehole, the same or different pipes may be used to transmit fluids, such as drilling mud, hydrocarbons, gas, or any other fluids or mixtures, from the borehole to the platform.
When conditions in the borehole are monitored, the data must be transmitted from sensors at or in the borehole to the processor that processes the data to generate data usable by a system or operator to provide data regarding characteristics in the borehole, to display the data, or to use the data to control operation of a downhole assembly, such as a drilling operation. In some cases, a borehole will be very far from a platform, such as 30 kilometers or more, and transmission of large amounts of data between a marinized assembly and the surface-based platform becomes difficult.
One type of monitoring and data communications system is distributed acoustic sensing (DAS) system. In such a system, a fiber optic wire is inserted into a borehole, a signal is transmitted into the fiber optic wire, and a reflected signal is detected to determine borehole characteristics. In a DAS system, a transmitter typically includes a laser and a pulse modulator and/or frequency modulator to generate the signal to be transmitted into the borehole. The transmitter also includes optics to control characteristics of the light emitted by the laser. A receiver includes one or more optical sensors, optics, and processing circuitry to process the detected reflected signals. However, DAS systems have a limited effective range due to signal losses over extended distances, particularly the distances that may be required to transmit signals between a platform and an undersea borehole.